scholarly journals Estimation of Possibilities of Using Fractal Dimension and Information Entropy of Elastic Waves for Assessment of Damage to Steel 20 at Low Cycle Fatigue

2021 ◽  
Vol 24 (3) ◽  
pp. 17-25
Author(s):  
A.A. Khlybov ◽  
Y.G. Kabaldin ◽  
M.S. Anosov ◽  
D.A. Ryabov ◽  
D.A. Shatagin ◽  
...  
Keyword(s):  
Fractal Dimension ◽  
Elastic Wave ◽  
Information Entropy ◽  
Low Cycle Fatigue ◽  
Experimental Studies ◽  
Ultrasonic Signal ◽  
Second Phase ◽  
Cycle Fatigue ◽  
Fatigue Damage Accumulation ◽  
Steel 20

The paper presents the results of experimental studies of specimens made of steel 20 for low-cycle fatigue (cantilever bending). A fatigue curve was obtained for the material under study in the range of stress amplitudes from 210 to 380 MPa. In logarithmic coordinates, this dependence is linear. According to the research results, it has been shown that one of the structure-sensitive characteristics is the shape of an elastic wave pulse transmitted through the medium under study. To analyze the pulse shape of an elastic wave, an algorithm is proposed for assessing the damage of materials, using the values of the fractal dimension of the attractor and the information entropy in the process of fatigue loading. It was found that according to the obtained dependences, the process of fatigue damage accumulation can be conditionally divided into 2 phases. In the first phase, the entropy of the ultrasonic signal practically does not change and remains within the range of 0.05-0.1 nat. The fractal dimension of the attractor of the ultrasonic signal increases from 1.5 to 1.8. During the transition to the second phase, the maximum values of the fractal dimension of the attractor of the ultrasonic signal are observed, the values of which decrease in the second phase to 1.4 before the destruction of the sample. The information entropy values in the second phase increase monotonically up to 0.55 nat. Studies have shown that the obtained dependences practically do not change with a change in the stress amplitude. The results of studies at various stress amplitudes have shown that the characteristics of the fractal dimension of the attractor and the information entropy of elastic wave pulses that have passed through the zones of accumulated damage in the metal expand and supplement the capabilities of acoustic methods in the problems of assessing the performance of materials with low-cycle fatigue and make it possible to identify the stage of destruction of steel 20.

The Revised Universal Slope Method to Predict the Low-Cycle Fatigue Lives of Elbow and Tee Pipes

2017 ◽  
Vol 139 (5) ◽  
Author(s):  
Hiun Nagamori ◽  
Koji Takahashi
Keyword(s):  
Experimental Data ◽  
Internal Pressure ◽  
Low Cycle Fatigue ◽  
Experimental Studies ◽  
High Accuracy ◽  
Universal Method ◽  
Cycle Fatigue ◽  
Element Analysis ◽  
Slope Method ◽  
Stress States

The stress states of elbow and tee pipes are complex and different from those of straight pipes. The low-cycle fatigue lives of elbows and tees cannot be predicted by Manson's universal slope method; however, a revised universal method proposed by Takahashi et al. was able to predict with high accuracy the low-cycle fatigue lives of elbows under combined cyclic bending and internal pressure. The objective of this study was to confirm the validity of the revised universal slope method for the prediction of low-cycle fatigue behaviors of elbows and tees of various shapes and dimensions under conditions of in-plane bending and internal pressure. Finite element analysis (FEA) was carried out to simulate the low-cycle fatigue behaviors observed in previous experimental studies of elbows and tees. The low-cycle fatigue behaviors, such as the area of crack initiation, the direction of crack growth, and the fatigue lives, obtained by the analysis were compared with previously obtained experimental data. Based on this comparison, the revised universal slope method was found to accurately predict the low-cycle fatigue behaviors of elbows and tees under internal pressure conditions regardless of differences in shape and dimensions.

Latest Development in Physics-Based Modeling of Coiled Tubing Plasticity and Fatigue

SPE Journal ◽  
2021 ◽  
pp. 1-12
Author(s):  
Zhanke Liu ◽  
Steven Tipton ◽  
Dinesh Sukumar
Keyword(s):  
Damage Accumulation ◽  
Low Cycle Fatigue ◽  
Experimental Investigations ◽  
Cycle Fatigue ◽  
State Variables ◽  
Coiled Tubing ◽  
Wall Thinning ◽  
Fatigue Damage Accumulation ◽  
Wide Range ◽  
Novel Algorithms

Summary Coiled tubing (CT) integrity is critical for well intervention operations in the field. To monitor and manage tubing integrity, the industry has developed a number of computer models over the past decades. Among them, low-cycle fatigue (LCF) modeling plays a paramount role in safeguarding tubing integrity. LCF modeling of CT strings dates back to the 1980s. Recently, novel algorithms have contributed to developments in physics-based modeling of tubing fatigue and plasticity. When CT trips into and out of the well, it goes through bending/straightening cycles under high differential pressure. Such tough conditions lead to low- or ultralow-cycle fatigue, limiting CT useful life. The model proposed in this study is derived from a previous one and is based on rigorously derived material parameters to compute the evolution of state variables from a wide range of loading conditions. Through newly formulated plasticity and strain parameters, a physics-based damage model predicts CT fatigue life, along with diametral growth and wall thinning. The revised modeling approach gives results for CT damage accumulation, diametral growth, and wall thinning under realistic field conditions, with experimental validation. For 20 different CT alloys, it was observed that the model improved in accuracy overall by approximately 18.8% and consistency by 14.0%, for constant pressure data sets of more than 4,500 data points. The modeling results provide insights into the nonlinear nature of fatigue damage accumulation. This study allowed developing recommendations to guide future analytical modeling and experimental investigations, summarize theoretical findings in physics-based LCF modeling, and provide practical guidelines for CT string management in the field. The study provides a fundamental understanding of CT LCF and introduces novel algorithms in plasticity and damage.

The influence of orientation on the elastic and low cycle fatigue properties of several single crystal nickel base superalloys

1994 ◽  
Vol 29 (2) ◽  
pp. 147-153 ◽  
Author(s):  
S X Li ◽  
E G Ellison ◽  
D J Smith
Keyword(s):  
Single Crystal ◽  
Low Cycle Fatigue ◽  
Experimental Studies ◽  
Elastic Response ◽  
Fatigue Properties ◽  
Elastic Behaviour ◽  
Nickel Base Superalloy ◽  
Cycle Fatigue ◽  
Nickel Base Superalloys ◽  
Nickel Base

Experimental studies on the influences of orientation on the elastic behaviour at 20°C and 950°C and the low cycle fatigue creep properties at 950°C of the single crystal nickel base superalloy SRR99 are described. The elastic response at 20°C is found to be in good agreement with predictions from the properties of pure nickel. At 950°C the orientation dependence is shown to be well correlated with a simple orientation function, which is also found to be insensitive to temperature. Similar correlations are shown for the single crystal nickel base superalloys PWA1480 and RENE N4 at high temperatures. The low cycle fatigue properties for fully reversed strain controlled cycles of SRR99 are shown to be strongly dependent on crystal orientation. Similar results from earlier work for RENE N4 are also illustrated. It is shown that by modifying the applied total strain range to take into account the influence of orientation for elastic deformation, essentially orientation-independent low fatigue cycle curves for SRR99 and RENE N4 are obtained.

SEM Study of Fatigue Crack Propagation in Chromium Martensitic Steel after LCF

2017 ◽  
Vol 754 ◽  
pp. 15-18 ◽  
Author(s):  
Tamaz Eterashvili ◽  
G. Abuladze ◽  
L. Kotiashvili ◽  
T. Dzigrashvili ◽  
M. Vardosanidze
Keyword(s):  
Fatigue Crack ◽  
Crack Propagation ◽  
Low Cycle Fatigue ◽  
Experimental Studies ◽  
Complex Problem ◽  
Fatigue Tests ◽  
Cycle Fatigue ◽  
Sem Study ◽  
Deformation Tests ◽  
Microstructure Of The Material

Crack propagation after low-cycle fatigue (LCF) deformation has been studied in the chromium martensitic structural steel. Although the study of a fundamental mechanism of fatigue crack growth has received much attention over the last decade, it still remains a sufficiently complex problem and needs full understanding. Moreover, the recent studies show that the cracks propagate discontinuously even on the millisecond timescale, and their growth rate significantly depends on a microstructure of the material. In the present work the boundaries of the former austenitic grains were revealed on the polished surfaces of the thermally treated samples, which subsequently were undergone low-cycle fatigue tests. The experimental studies show that fatigue macrocracks mainly grow along the boundaries of the former austenitic grains, and changetheir propagation direction when crossing the grain boundary, however, remain within 45 ̊ interval with regard the cycling axis. In particular cases, when the boundaries of a martensite packets and those of the former austenite grains lay along the length of a packet, the macrocrack is better formed and with regular borders. After a macrocrack reaches a definite length ~30-50μ, a microcrack is nucleated ahead of the macrocrack tip, and is oriented along the substructure element of the steel. Further deformation tests provide an increase in the length of the main crack via aggregation of microcracks initiated ahead of it during the LCF. In the cases when the macrocrack is deviated, slip bands are formed in martensitic structures along the boundaries of martensite packets (laths). A correlation is revealed between the microcrack components and the substructure elements of the steel as well. The same results were obtained by fractography of the tested and fractured samples. However, in the latter case correlation was established between the cleavage facets and the dimensions of packets.

Latest Development in Physics-Based Modeling of Coiled Tubing Plasticity and Fatigue

2021 ◽  
Author(s):  
Zhanke Liu ◽  
Steven M. Tipton ◽  
Dinesh Sukumar
Keyword(s):  
Damage Accumulation ◽  
Low Cycle Fatigue ◽  
Experimental Investigations ◽  
Cycle Fatigue ◽  
State Variables ◽  
Coiled Tubing ◽  
Wall Thinning ◽  
Fatigue Damage Accumulation ◽  
Wide Range ◽  
Novel Algorithms

Abstract Coiled tubing (CT) integrity is critical for well intervention operations in the field. To monitor and manage tubing integrity, the industry has developed a number of computer models over the past decades. Among them, low-cycle fatigue (LCF) modeling plays a paramount role in safeguarding tubing integrity. LCF modeling of CT strings dates back to the 1980s. Recently, novel algorithms have contributed to developments in physics-based modeling of tubing fatigue and plasticity. As CT trips into and out of the well, it goes through bending-straightening cycles under high differential pressure. Such tough conditions lead to low- or ultralow-cycle fatigue, limiting CT useful life. The model proposed in this study is derived from a previous one and based on rigorously derived material parameters to compute the evolution of state variables from a wide range of loading conditions. Through newly formulated plasticity and strain parameters, a physics-based damage model predicts CT fatigue life, along with diametral growth and wall thinning. The revised modeling approach gives results for CT damage accumulation, diametral growth, and wall thinning under realistic field conditions, with experimental validation. For 20 different coiled tubing alloys, it was observed that the model improved in accuracy overall by about 18.8% and consistency by 14.0%, for constant pressure data sets of more than 4,500 data points. The modeling results provide insights into the nonlinear nature of fatigue damage accumulation. This study allowed developing recommendations to guide future analytical modeling and experimental investigations, to summarize theoretical findings in physics-based LCF modeling, and to provide practical guidelines for CT string management in the field. The study provides a fundamental understanding of CT LCF and introduces novel algorithms in plasticity and damage.

Influence of addition of aluminum on the low-cycle fatigue of steel 20 �ShL in certain media

1979 ◽  
Vol 15 (3) ◽  
pp. 309-310
Author(s):  
A. B. Kuslitskii ◽  
V. L. Mizetskii ◽  
M. F. Yasinskii
Keyword(s):  
Low Cycle Fatigue ◽  
Cycle Fatigue ◽  
Steel 20
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